Interfacial Structure-properties Relationship Of Functionalized Carbon Nanotube/Epoxy Composites

Carbon nanotube (CNT) has been extensively studied in the area of polymer-based composites, due to its extraordinary mechanical, thermal and electrical conductive properties. The bad dispersion state of CNT in polymer matrix and the poor interfacial interaction between CNT and polymer matrix are the main drawbacks which greatly affect the final properties of CNT/polymer composites. However, surface functionalization of CNT is an effective way to solve these two problems. In this dissertation, epoxy resin was used as the polymer matrix and different surface functionalization methods had been taken to produce different kinds of functionalized multi-walled carbon nanotubes (MWNTs), which were then compounded with epoxy resin to produce MWNT/epoxy composites. Systematical analysis had been taken to clarify the effects of the dispersion of functionalized MWNT in epoxy matrix and the interfacial interaction between the functionalized MWNT and epoxy on the properties of MWNT/epoxy composites.Firstly, MWNT was successfully functionalized with hyperbranched poly(urea-urethane)s (HPU) to produce MWNT-HPU, and was then compounded with CYD-128 epoxy resin to fabricate MWNT-HPU/epoxy composites. The effect of the HPU surface functionalization on the dispersion of MWNT in epoxy matrix and the effect on the processing, flexural and dynamic mechanical, thermal and electrical conductive as well as thermal stable properties of the composites were studied. The results showed that the dispersion of MWNT in epoxy matrix and the interfacial interaction between MWNT and epoxy were improved via HPU functionalization. Herein, the rheological properties of the un-cured MWNT/epoxy suspensions, and the flexural and dynamic mechanical as well as thermal stable properties of final composites were greatly enhanced. In addition, the HPU functionalization also realized a better phonon coupling between MWNT and epoxy, thus effectively reduced the interfacial thermal resistence and improved the thermal conductive properties of the composites. HPU surface functionalization also effectively reduced the chance of electron transportation in the composites, and endowed the composites with high electrical resistivities. Secondly, controlled and uniform silica coating on MWNT was successfully achieved via sol-gel process to fabricate silica coated MWNT coaxial nanocable (SiO2@MWNT).Then, SiO2@MWNT hybrid fillers were compounded with CYD-128 epoxy resin to fabricate SiO2@MWNT/epoxy composites. The effect of the SiO2 coating layer on the flexural and dynamic mechanical, thermal and electrical conductive as well as thermal stable properties of the composites were studied. The results showed that aggregates of MWNT were greatly reduced to realize good dispersion of MWNT in epoxy matrix and the interfacial interaction between MWNT and epoxy matrix was improved. Hereby, the flexural and dynamic mechanical, as well as thermal stable properties of the composites were enhanced. Moreover, the SiO2 coating layer also realize the modulus matching between stiff MWNT and soft epoxy matrix to reduce the interfacial thermal resistance, as a result of which, the final thermal conductivities of the composites were obviously increased. Simultaneously, the electrical insulating SiO2 layer also provided the SiO2@MWNT/epoxy composites with high electrical resistivitites.Moreover, controlled and uniform titania coating on MWNT was also successfully achieved via sol-gel process to fabricate titania coated MWNT coaxial nanocable (TiO2@MWNT). Then sintering procedure was taken to produce a crystallized anatase coating layer.In the final part, TiO2@MWNT was compounded with CYD-128 epoxy resin to fabricate TiO2@MWNT/epoxy composites. The flexural mechanical, thermal and electrical conductive properties of the TiO2@MWNT/epoxy composites were studied. The TiO2 coating layer improved the dispersion of MWNT in epoxy matrix. Herein, the flexural strength and modulus of the composites were obviously improved. In addition to alleviate the modulus mismatching between stiff MWNT and soft epoxy matrix, the instinct relative high thermal conductivity of crystal TiO2 coating layer could make another contribution to the improvement of thermal conductivities of the TiO2@MWNT/epoxy composites. The electrical insulating TiO2 layer also provided the composites with nearly the same electrical resistivities as that of neat epoxy.